AKT. 9 A POLLACK WHALE FROM FLORIDA MILLER. \) 



to alterations in the position of the anterior process, since the rela- 

 tionship of the posterior process to the cochlear mass is essentially 

 identical in the two types of periotic. The anterior process, however, 

 is so placed in the right whale that its axis is about parallel to a pro- 

 longation of that of the internal acoustic meatus, while in the fin- 

 backs and humpback its axis forms at least a right angle with the 

 prolonged axis of the meatus. Another peculiarity of the periotic 

 in the right whale is the relatively small size of the cochlear mass, 

 a character which is not readily described, but which is immediately 

 apparent on comparison of the periotic of a right whale with that 

 of the humpback or of any of the finbacks. 



Among the Balcenopteiidoi the genus Megaptera appears to be 

 distinguished by a conspicuous tendency toward heightening the 

 cochlear portion of the periotic, so that the orifices appear to stand 

 at the base or on the side of a nearly perpendicular wall, while in 

 the finbacks they are situated on an oblique or nearly horizontal 

 surface. In Balcenoptei'a physalus the orifices of the internal acoustic 

 meatus and the facial canal are separated from each other by a 

 mass of bone whose diameter is fully as great as that of the canal, 

 a peculiarity which appears to be diagnostic of the species. The 

 opposite condition is seen in BaUeTioptera acutorostrata^ in which 

 the two orifices lie at the bottom of a common pit or tube with no 

 definite septum between them. A well-developed but narrow septum 

 is found in Balo'noptera horealis and Sihhaldiis viusmdus, but the 

 periotic bones of these two animals are readily distinguished by the 

 different development of the fossa for the stapedial muscle, this fossa 

 having a very narrow, contracted area in B. horealis, while in 

 Sihhaldus it is of the normal widelj' spread type. 



The material examined (representing four individuals of Eiiba- 

 lana^ two of Megaptera^ three of Bcdodnopfera physcduH^ two of B. 

 acutorostrata, one of B. horealk^ and two supposedly Sihhaldus) 

 is not sufficiently exteusive to form the basis of any generalizations 

 as to the true value of all the characters which I have mentioned, 

 but it appears to be reasonably probable that most of these peculiar- 

 ities represent features which are constant. Assuming that they 

 have a definitely taxonomic value, the characters of the ear bones 

 in the baleen whales of the North Atlantic may be arranged as 

 follows : 



Axis of anterior petrous process approximately parallel with axis of internal 

 acoustic meatus ; axes of anterior and posterior petrous processes converging 

 at an angle much less than a right angle ; auditory region proper relatively 

 small ; tympanic squai-ish or irregularly rhomboidal in outline Balaenidae. 



Axis of anterier petrous process approximately at right angles with axis of in- 

 ternal acoustic meatus ; axes of anterior and posterior petrous processes con- 

 verging at an angle obviously greater than a right angle; auditory region 

 proper relatively large; tympanic ovate in outline Balsenopteridae. 



